Magnetic alarm switch



Nov. 22, 1949 v s 2,489,113

MAGNET IC ALARM SWITGHS' Filed May 21, 1947 2 Sheets-Sheet l 1 N VENTOR. Gemge L wewazfww Nov. 22, 1949 G. L. VEENSTRA MAGNETIC ALARM SWITCHFiled May 21, 1947 2 Sheets-Sheet 2 I 2 W 0 amxg Patented Nov. 22, 1949UNITED STATES PATENT OFFICE 4 Claims.

This invention relates to alarm devices and more particularly tomagnetic devices adapted to close an electrical circuit when a body ofiron approaches.

My new device is especially suitable for use in connection with gasolineservice stations whereby the attendant is apprised of the approach of anautomobile so that he may come to the pumps and service the automobile.

There have been many types of devices whose purpose was the same as thatof my new device, but the manners of operation of these prior deviceshave been such that many disadvantages have been inherent therein. Twogeneral types of devices have been the mechanical contact type and thepneumatic type. In the case of the mechanical type, the weight of theautomobile was used to mechanically move two electrical contactstogether thereby completing an alarm circuit. The pneumatic typeoperated by having the weight of the automobile depress a tube andthereby cause the air pressure therein to increase, operating adiaphragm mechanically connected with the contact closing device of theelectrical system.

In both of these types of devices it has been required that there be aportion of the system adapted to be run over by the automobile. Thus allapproaches to the service station had to be provided with members whichwere required to be of such size that they were certain to be engagedwhen the automobile or other vehicle entered the service stationdriveways. In the case of the mechanical devices wear and tear was aconsiderable problem, and in the case of the pneumatic system,maintaining air tight connections was a problem. The pneumatic systemsare sensitive and will cause an alarm when a person steps on same, andthus cause much confusion.

My new device is not intended to be engaged. It is only necessary for alarge mass of iron, such as an automobile or the like to pass within acertain pre-determined distance of the device in order that an alarm begiven. No apparatus other than a single member of comparatively smallsize is installed at key positions, the electrical connections theretobeing hidden if desired, since they are not intended to be run over bythe automobiles. No pneumatic or mechanical systems are used, nor isthere any wear on any of the parts of my device.

My device operates on old and well-known principles, but the applicationthereof in the instant case is novel. A magnetic member is oriented inthe earth's field at any given position of the service station and isadjusted so that when there are no automobiles in the vicinity of thesame it will remain in a given position. In the event that an automobileapproaches, the earth's field will be disturbed and the magnetic memberwill swing in one direction or another, and in so doing cause engagementbetween a pair of electrical contacts. This engagement may control analarm or indicating circuit if desired.

It is accordingly the primary object of my invention to provide a devicefor warning of the approach of a large mass of iron, comprising a devicenormally quiescent when the earths field in its immediate vicinity isnormal, but serving to cause an alarm to operate if the earths fieldthereabout is disturbed.

A further object of the invention is to provide a device of thecharacter described in which the same is not intended to be engaged orrun over by automobiles while warning of their approach.

Still further objects of the invention are to eliminate thedisadvantages above referred to in connection with other devices andprovide the advantages stated in connection with my magnetic device.

Other objects of the invention are to provide a device of the characterdescribed which can be used on any type terrain, which is Weather-proof,sturdy, durable, and compact.

With the foregoing and other objects in view which will appear as thedescription proceeds, the invention consists of certain novel featuresof construction, arrangement and a combination of parts hereinafterfully described, illustrated in the accompanying drawings, andparticularly pointed out in the appended claims, it being understoodthat various changes in the form, proportion, size and minor details ofthe structure may be made without departing from the spirit orsacrificing any of the advantages of the invention.

For the purpose of facilitating an understanding of my invention, I haveillustrated in the accompanying drawings a preferred embodiment thereof,from an inspection of which, when considered in connection with thefollowing description, my invention, its mode of construction, assemblyand operation, and many of its advantages should be readily understoodand appreciated.

Referring to the drawings in which the same characters of reference areemployed to indicate corresponding or similar parts throughout theseveral figures of the drawings:

Fig. 1 is a diagrammatic view illustrating the manner of installing mynew device.

Fig. 2 is a top plan view of my device showin its appearance wheninstalled on the to of the ground.

Fig. 3 is a sectional view through the same taken along the line 3-3 ofFig. 4 and in the indicated direction.

Fig. 4 is a sectional view taken along the line 4- l of Fig. 2 and inthe indicated direction.

Fig. 5 is a top plan view of my device with the cover plate and theadjustment plates removed.

Fig. 6 is a sectional view taken through the magnetic portion of mydevice along the line 6-E of Fig. 5 and in the indicated direction.

Fig. 7 is a bottom plan view of the magnetic element of my device.

8 is a sectional view of one of the portions of my device taken alongthe line 8-8 of Fig. 5 and in the indicated direction.

Fig. 9 is a perspective view of the sensitive contact of m device.

Fig. 10 is a sectional view on a considerably reduced scale takenthrough one of my devices showing the manner of installing same belowthe surface of the driveway.

Fig. 11 is a top plan view of a modified form of the movable magneticelement of m device.

The reference character designates generally the driveway of a gasolineservice station having 7 one or more of my new devices, designatedgenerally 2|, installed thereat. The station building is designated 22and the pump island 23. As shown in Fig. l, the approach of anautomobile 24 causes the device 2i to close the circuit in which same isconnected. The leads from the device 2i pass through a conduit 18 whichmay be above or below the driveway 20. and into the building 22. Atypical installation will include a relay 2B, in series with a battery27 and the device 2| so that the contacts of the relay 26 may operate ahigher power alarm or indicating circuit designated 28 in the drawing.

The device 2| is shown in the drawings as a disc member 29 having abeveled edge as shown at 3B. The disc is formed of some non-magneticmaterial such as brass or the like and is provided about its peripherywith passages 3| extending through the same whereby the device 2| may befastened down as for example by the screws 32. The heads of the screws32 are adapted to be seated in recesses 33 provided therefore in thebeveled edge 30. The purpose of the beveled edge 36 is to permitvehicles easil to ride upon and over the device 2i in case same isinstalled on the surface of the ground in the path of travel of saidvehicles.

On the interior of the disc and concentrically therewith is formed acylindrical cavity 34 which carries the operating portion of m alarmdevice. The upper edge of the cavity 34 is provided with a set-backshoulder 35 for seating a cover glass 36 and a gasket 31. The gasket 37besides serving as a cushion for the cover glass 36 serves to render thechamber or cavity 34 waterproof. A second set-back portion or shoulder38 is provided above shoulder 37, the shoulder 38 being intended tocarry the metal cover plate 39 and its gasket 46. The gasket 4!} aids inrendering the cavity 34 waterproof in cooperation with gasket 3], bothof said gaskets being formed of any suitable soft lient material such asfor example rubber. r of the gaskets may be eliminated, if desired, inthe interests of economy.

The cover plate 39 is intended to be held in position by means of aplurality of screws 4| which pass through the plate 39 and engage inappropriate screw threaded holes provided in the shoulder 36. The screwheads of screws 41 are preferably flat and countersunk into the platemember 39 so as to present a smooth surface on the top of the device 2I. The cover plate and all screws and metal fittings of the device, asthus far described are made out of the same nonmagnetic material fromwhich the disc member 29 is formed.

Mounted upon the bottom wall 42 of the cavity 34 is a plate member 43attached by means of the screw 44. Said plate member carries a pin 45having a needle bearing point 46 which carries balanced thereupon anon-metallic, freely rotatable generally cylindrical member 47. Saidmember 4'! is provided with a centra1 cavity 48 having a depression 49at the inner end thereof in order to cooperate with the needle point 46.It will be noted that the center of gravit of the member 41 isconsiderably below the point of engagement of the recess 49 and thepoint 46 in order that the member ll will readily balance and rotateupon said point. The member 41 carries upon the bottom surface thereof apair of bar magnets 50 and El on opposite sides of the buttom surface ofthe member 41. Said bar magnets are formed of a highly paramagneticalloy, such as for example the ferrous alloy known in the trade asAlnico. The bar magnets 59 and 5! may be attached by any suitable meanssuch as for example cement or the like, or may be forced into cavitiesformed therefor in the member 4i. If desired, in the case the member 41is formed from a condensate product or resin, the bar magnets may bemolded thereinto during formation.

It will be seen from the above description that the mounted member 41and magnets 50 and Si constitute a compass and the combined field of themagnets will orient itself to a position of equilibrium with respect tothe earths magnetic field, or the field of any adjacent electromagneticinfluence by swinging the member 4'] about the pin point bearing 43. Itshould be noted that the ends of the magnets 50 and SI protrude asubstantial distance outwardl from the member 41 for a purpose presentlyto be described.

Diametrically opposite to the member 41 a block member 52 is mounted onthe bottom wall of the cavity 34. Said block member formed of insulatingmaterial and is attached to the wall 42 by means of a screw 53 whichengages a central passageway in the block and an appropriatescrew-threaded opening in the disc member 29. A resilient member 54 iscarried by said block member insulated from the wall of the member 29said resilient member being oriented to extend between the bifurcationcomprising the ends of the magnets 58 and 5%. A preferred constructionof the block member 52 is shown in the drawings. There are providedupper and lower portions 55 and 56, the upper portion having a boss 5?so that an annular space is formed between the two portions whenassembled, the screw 53 being insulated from the annular space.

As will be seen in Fig. 9, the member 54 comprises a strip of metal ofgenerally L-shaped formation having a right angle bend on the one endthereof, the opposite end 59 being free and carrying a contact pointBill which is set back from the free end 59 and engageable from bothsides of the meta1 strip. The shank of the free end 59 of the member 54narrows down at 5i so that the end 59 will be highly flexible andsensitive.

The bent portion is provided with an opening 92 intended to fit the boss51 so that the member 54 can be fixed to the block. The base portion 93which is at right angles to the bent portion and is in the same plane asthe end 59 and portion 6! is arranged to engage the side of the blockmem ber 52 to prevent rotation of the member 54 with respect to saidblock. Obviously, loosening the screw 53 will permit the block 52 andmember 54 to be rotated so that the position of the end 59 withrespectto the magnets 59 and 5| may be adjusted. Likewise, if desired theentire block 52 and member 54 may be replaced.

The bent portion is provided with a lug 94 to which an electrical lead95 is soldered. The opposing end of the lead 65 is provided with apierced lug 99 engaging the conducting member 61 which extends into thecavity 34 and being held thereto by the nuts 98 and 99. The member 9?may be in the form of a threaded rod which extends from the recess 19formed on the periphery of the member 29 in the beveled edge 39, throughthe wall of the member 29 and into the recess 34. Said member 9? isinsulated from the member 29 by means of the sleeve H and the washers l2and 13, said washers and sleeves being formed from insulating material,and serving as well as waterproofing means to prevent the entrance ofmoisture into the cavity 34. At the opposite end of the member 91, Ihave connected an electrical lead 74, same being held in place 4 uponthe threaded end of the rod Bl by nuts 15 and 16. The lead 14 isprotectively insulated except at point of electrical contact and extendsthrough an opening H provided in the bottom of the recess 19 and thenceinto a conduit 18 or the like to the station house as described.

The cavity 19 is provided with a binding post 19 to which iselectrically connected a second lead 89 which also passes out of thecavity 19 through the opening '5'! and enters the conduit 18 leading tothe station house. This lead is grounded to the member 29.

The cavity 19 has a pair of shoulders 8| and 82 at the sides thereofadapted to seat thereon a cover plate 83 held in position by screws 84passing through appropriate openings in said cover plate and screwthreaded into said shoulders 8| and B2. The cover plate 83 conforms tothe contours of the device 2! and the screws 84 are countersunk topresent a smooth unobstructive surface.

A second cavity 95 is formed on the periphery of the member 29 oppositeto the cavity 19. This cavity 85 is also provided with shoulders asshown at 89 and 87 and has a cover plate 88 held in position by screws99. It may be smaller in size than the cavity 19.

From each of the cavities 79 and 85 there extends a screw threadedmember 99 and 9| through the walls of the member 29 and into the cavity34. The outer ends of the members 99 and 9| are slotted as shown at 92and 93 respectively, and the inner ends of the members are formed aselectrical contacts 94 and 95 respectively. The members 99 and 9|electrically engage the disc member 29 but are each provided with somemeans for preventing moisture entering the cavity 34. or packing asshown at 99 and 91. The contacts 94 and 95 are arranged to be juxtaposedon opposite sides of the member 54 and aligned with the contact 99 sothat if the free end 59 is swung to either side it will cause engagmentbetween the contact 69 and one of the contacts 94 or 95. The distancebetween the contacts 94 and 95 is adjust- This may take the form ofwashers.

able by screwing or unscrewing the members 99 and 9| with a screwdriver, using the slotted ends 92 and 93.

In the installation of my new device, a recess may be dug in thepavement as shown at 98 to accommodate the outgoing wires in case thedevice 2| is installed on top of the pavement and the conduit 18 alsolaid on top of the pavement, or else a cavity 39 may be formed and theentire device sunk below the surface and covered with paving materialwith the exception of the three cover plates 39, 83, and 98. Theconstruction of my device makes it highly adaptable to almost anycondition of pavement or ground and the exact manner of installation isimmaterial insofar as the claimed invention is concerned.

My device operates in the following manner:

Initially the device 2| is installed and oriented so that the neutralposition of the member 54 is precisel between the magnets 59 and 5| asshown in Fig. 5. Since all of the station equipment, such as the pumpsof the pump island 23, the station building 22, etc. are in place, thisorientation properly compensates for magnetic deviation. In the eventthat a vehicle such as an automobile 24 passes near the device, thecompass will swing and one or the other of the magnets 59 or 5| willengage the free end 59 of the member 54 moving the contact 69 againsteither the contact 94 or the contact 95. By proper adjustment of themembers 99 and 9| the distance within which the vehicle must come inorder to cause such engagement can be adjusted.

The form of the member 54 is an important feature of m invention. Themember is made from highly resilient spring meta1 such as for examplePhosphor bronze so that it will readily return after being deformed. Thelarge end portion 59 carrying the contact 99 serves to give the memberinertia so that when struck by the moving magnet it will swing in a widearc. The narrow portion 99 increases the sensitivity of the member 54 sothat very little moment is required to move the same, although theresilient quality is still present. As a result of this construction,the approach of the automobile will cause the contact 99 to onlymomentarily engage say the contact 94 due to the inertia of the end 59,said end then swinging back due to the resilence of the portion 6| to anon-engaging position. This causes only a short completion of thecircuit as will be explained, so that the alarm will not ringcontinuously if an automobile approaches the device 2| and stops there.Naturally by proper adjustment of the members 99 and 9| a continuousengagement may be obtained if desired, but the above describedarrangement is believed preferable.

When the contact 99 engages the contact 94 the following circuit iscompleted; wire ll, member 61, lug 99, lead 65, lug 94, member 54,contact 69, contact 94, member 90, disc member 29, binding post 19, andwire 89. The wires 11 and 89 are connected to some alarm or indicatingcircuit as diescribed which may light a lamp or ring a bell, e c.

Once the device has been installed, adjustments to the members 99 and 9|may be made b removing the cover plates 83 and 88. The removal of thelarge cover plate 39 permits the interior of the recess 34 to be seenthrough the cover glass 36. It should be noted that adjustments can bemade to the plate member 43 to re-orient the position of the pin 45, andto the block member 52 as explained above. It should also be appreciatedthat all of the various parts of the device can readily be removed andreplaced or repaired.

If desired, the members 99 and SH need not be grounded but may beconnected to different alarm circuits whereb the location of anapproaching vehicle may be determined from the alarm. It should also beapparent that the application of my device is not limited to servicestations but may as well be made in any arrangement where it is desiredto warn of the approach of bodies of ferrous metal.

Certain terms are used in the claims appended hereto which are intendedto convey broad connotations rather than the narrow interpretationsapparently assigned thereto. The term magnet is not intended to mean asingle magnetic member but also extends to a group or plurality ofmagnetic members producing a resultant field. Obviously there will be astructure of a single member capable of producing said field. In thecase of the Word bifurcation it is intended that the use of any forkedmember or extension of the rotatable member 41 be included. In thepreferred structure the magnetic members 50 and form the bifurcation butthis is not essential to the operation of the device.

In line with the above, there is shown in Fig. 11 a modified form of themoving member designated 41' corresponding in function to member 41.Said member 4'! carries two permanent magnets 50 and 5| molded thereintoand has a bifurcation which is actually a slot cut into an edgepresenting its opposite sides H6 and III to the free end of theresilient member 54.

It is believed that my invention, its mode of construction and assembly,and many of its advantages should be readily understood from t eforegoing without further description, and it should also be manifestthat while a preferred embodiment of the invention has been shown anddescribed for illustrative purposes, the structural details arenevertheless capable of wide variation within the purview of myinvention as defined in the appended claims.

What I claim and desire to secure by Letters Patent of the United Statesis:

1. In a device for detecting the approach of vehicles having ferrousparts in a driveway and comprising a housing having a magnet thereinadapted to swing when a vehicle approaches for closing an electricalcircuit, the herein described invention which consists in said magnetbeing mounted for rotation in a horizontal plane un der the influenceonly of the resultant magnetic field of the earth at the locality of thedevice, bifurcated prodding means carried by said magnet, a resilientcontact member attached to said housing and connected to said circuitand having its free end disposed between the bifurcations, the housingbeing oriented relative to the said resultant field normally to bepoised with the said free end of the contact member clear of thebifurcations when no vehicle is in the vicinity of the device, a pair ofmembers attached to said housing and presenting electrical contacts toopposite sides of said resilient member and being connected to saidelectrical circuit, the swinging of said magnet serving to move the endof said resilient member against one or the other of said contacts.

2. In a device for detecting the approach of vehicles having ferrousparts in a driveway and comprising a housing having a magnet thereinadapted to swing when a vehicle approaches for closing an electricalcircuit, the herein described invention which consists in said magnetbeing mounted for rotation in a horizontal plane under the influenceonly of the resultant magnetic field of the earth at the locality of thedevice, bifurcated prodding means carried by said magnet, a resilientcontact member attached to said nousing and connected to said circuitand having its free end disposed between the bifurcations, the housingbeing oriented relative to the said resultant field normally to bepoised with the said free end of th contact member clear of thebifurcations when no vehicle i in the vicinity of the device, a pair ofmembers attached to said housing and presenting electrical contacts toopposite sides of said resilient member and being connected to saidelectrical circuit, the swinging of said magnet serving to move the endof said resilient member against one or the other of said contacts, saidpair of members being adjustable to move the electrical contacts on aline tangentially to the movement of the bifurcated prodding memberwhereby the distance which the free end of the resilient member mustmove prior to engaging either said electrical contacts may be varied.

3. In a device for detecting the approach of vehicles having ferrousparts in a driveway and comprising a housing installed in the drivewayand having a magnet therein adapted to move when a Vehicle approachesfor closing an electrical circuit, the herein invention which consistsof said magnet being mounted for free rotation for a limited extent in ahorizontal plane and being under the influence only of the resultantmagnetic field of the earth at the location of the device, an elongatedresilient member having one end insulatedly mounted within the housingand fixed relative to the magnet, a pair of juxtaposed contacts onopposite sides of the resilient member and normally not engaged thereby,said electrical circuit adapted to be closed upon engagement of theresilient member with either of the contacts and opened upon cessationof said engagement, means carried by the magnet normally poised onopposite sides of the free end of the resilient member Without touchingthe same, but adapted upon swinging of the magnet in either directioncaused by the approach of a vehicle momentarily to engage one side ofthe said. end of the said resilient member to move said resilient memberto engage one of said electrical contacts.

4. In a device of the character described, comprising a housing adaptedto be positioned relative to a driveway where the approach of vehicleshaving,- ferrous parts will be detected, an electrical circuit adaptedto be closed by the approach of vehicles adjacent the housing, and saidhousing having therein a pivoted magnet; the invention herein describedwhich. comprises prodding means carried by said magnet, a resilientcontact member carried by the housing and adapted to be engaged by theprodding means, electrical contacting means adapted to be engaged by theresilient contact membe to close said electrical circult, said magnetbeing mounted for rotation in a horizontal plane under the influenceonly of the resultant :na .netic field of the earth at the 10- cality ofthe device, said prodding mean normall being free of said resilientcontact men:- whereby approach of a vehicle will disturb the aid rultant field and cause the swingof prodding means into engagement withthe resilient member to move same against the electrical contactingmeans closing said circuit,

the magnet strength and the rigidity of the resilient member being suchthat only momentary contact will be made upon said approach, Whereby theapproach of additional vehicles Will result in additional momentaryclosings of the circuit, 5 said prodding means including a pair ofjuxtaposed engagement portions, said free end of said resilient memberbeing disposed between said portions. 10

GEORGE L. VEENSTRA.

REFERENCES CITED The following references are of record in the 15 fileof this patent:

Number Glennon et al Mar. 26, 1946

